1. Field of the invention
This invention relates to a spot welding electrode and an electrode tip, more particularly to an improvement in a spot welding electrode and an electrode tip used for a spot welding machine.
2. Description of the Prior Art
A typical conventional spot welding electrode comprises, as shown in FIG. 8, a shank 1a with a longitudinal hollow part provided therein with a cooling water pipe 4a adapted for supplying cooling water, and an electrode tip 5a dismountably fixed on the end of the shank 1a. The cooling water is supplied through the water pipe 4a and directly cools the electrode tip 5a from inside so as to prevent undesirable deformation of the electrode tip 5a because of to the welding operation.
Since it is likely that an end portion of the electrode tip 5a is worn because of to repeated welding operations, the electrode tip 5a should be frequently ground after it has been removed from the shank, or should be replaced by a new one, while stopping the cooling water supplied from the cooling water pipe 4a.
However, the spot welding electrode of this type is disadvantageous in the fact that since the electrode tip 5a is directly cooled by supplying the cooling water to the inside of the electrode tip 5a, the cooling water remaining in the shank 1a may leak to the outside and wet the working place, and thus cause rust to be developed on an object to be welded. To clean up the leaked water for further welding operation, time-consuming work becomes necessary.
Japanese Utility Model Registration Application Laid-open No. 62-3290 proposes, as a countermeasure against water leakage upon exchange or falling off of a spot welding electrode provided a water check valve at the exit of the water supply pipe, which functions such that it keeps opening while the electrode tip is mounted and automatically closes when the electrode tip is removed. This mechanism, however, cannot completely prevent water leakage and requires a complex structure, thereby causing disadvantages with respect to cost and maintenance work.